This invention relates to a laser-machining optical apparatus for working, by using convergent laser light in high energy density, an object having a worked area greater than the size of a cross-section of the laser light at a high efficiency.
As one of the methods most generally used to remove or work an object by utilizing energy of laser light, a method is known which is based on removing the material of a specimen by a thermal or chemical action caused by irradiating a specimen surface with a laser light beam which is converged to increase the energy density. A method, such as that disclosed on pages 17 to 23 of SPIE, Vol. 988 (1988), is also known in which an image of a mask having a working pattern formed on its surface is projected onto a surface of a specimen so that a surface region thereof having an area corresponding to the sectional area of a laser beam or an area defined by optically enlarging or reducing the sectional area of the laser beam can be worked at one time. There is also a method in which a large area of an image of a working pattern on a mask is collectively projected to an object formed of a material reactive with light through a laser light beam having an increased sectional area. This effect may be achieved by excimer laser exposure. Ordinarily, in the case of working an object formed of a material non-reactive with light by laser energy, there is a threshold value of the energy density at which the material can be removed. Accordingly, in the method of removing the material of an object by using the abovementioned mask, if the transverse sectional area of the laser beam is increased to set a large area through which the object can be worked at one time, the energy density may be so low that the object cannot be worked. Naturally, there is a limit of the increase in the beam area. For this reason, in the case of applying the method of working a specimen by projecting a pattern on a mask to the specimen surface to a process using a large-area working pattern, it is a common practice to use a step-and-repeat process in which a local region of the specimen is worked with a small-area laser beam and the mask and the specimen is thereafter moved to work another region. Conventionally, a method of moving the laser beam or moving the mask and the specimen relative to the laser beam is not used in such a case.
On the other hand, as a method of working an object by projecting a large-area working pattern through a laser beam, a method, such as that described on pages 149 to 152 of CHEMITRONICS, Vol. 4 (1989.9), is known in which a thin-film metal mask is formed on a surface of a specimen by photochemical exposure, the specimen is moved while the specimen surface with the mask is irradiated with a convergent laser beam to work the material, and the mask is thereafter removed by being chemically etched.
The above-described conventional methods achieve a high working efficiency but require a long total processing time through the entire process, because of the need for a photochemical exposure step for forming the mask. They also entail the risk of damage to the mask because the mask is irradiated with the laser beam having the same energy density as that required for removing the material.